--> Abstract: Knickpoint Migration in Deepwater Channels in Response to Fold Growth in Compressional Settings: Examples from the West Niger Delta, by Paivi Heinio Richard Davies; #90039 (2005)

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Knickpoint Migration in Deepwater Channels in Response to Fold Growth in Compressional Settings: Examples from the West Niger Delta

Paivi Heinio Richard Davies
Cardiff University, Wales, United Kingdom

Deepwater sedimentation patterns in compressional settings, such as foreland basins, trenches and some passive margins are complicated by the contemporaneous growth of compressional folds. 3D seismic data from the ultra-deepwater compressional domain of West Niger Delta reveal sinuous channel-levee systems and their interaction with actively growing folds. Four responses to fold growth are recognised: (a) upslope migration of knickpoints, (b) channel diversion, (c) changes in morphometrics, such as channel-belt width and meander wavelength and (d) no measurable response.

We describe knickpoint migration as a result of fold growth in one channel system that has undergone a complex history of aggradation and degradation. The channel system has a 1.5-4 km wide channel-belt, which consists of inner levee terraces confined by prominent outer levees. The present, c. 60 m wide channel thalweg is entrenched c. 140 m below the outer levee crests and has a gradient of c. 0.5°. Two knickpoints along the channel are marked by sharp increases in dip (up to c. 5°) and wide, low-gradient thalwegs upslope of them. These are revealed by detailed morphometric measurements of the channel-belt dimensions. The knickpoints can be linked to the growth of particular thrust-propagation anticlines and mark specific positions along the fold uplift.

Knickpoint migration is well studied facet of fluvial environments. This represents one of the first detailed descriptions of their submarine equivalents. We predict that repetitive knickpoint migration is an intrinsic characteristic of deepwater channel development in compressional settings and will result in multiple erosion surfaces and complex channel fills.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005